1. Field of the Invention
The invention relates to a moisture-curing coating composition comprising a silane-terminated polymer and to a method for sealing surfaces.
2. Description of the Related Art
It is massively important to seal organic and inorganic building materials such as wood or concrete internally and externally on buildings or on the roof, against the penetration of water, in order to prevent destruction of the materials over time.
On complex roofs with copious detailing, many sealing materials frequently used in the past, such as bitumen sheets, have almost entirely disappeared, on account of the very great difficulty of sealing angles and edges. This problem was subsequently solved by the use of molten bitumen, but only at the expense of other hazards for the operator, through toxic vapors and through operation with the very hot liquid. VOC limitations and toxicological considerations have seen other solutions formerly in use, such as solvent-borne bitumen systems, being replaced by different technologies.
Nowadays, water-based coating materials such as acrylate-modified or polymer-modified bitumen emulsions are used primarily, although one- and two-component polyurethane systems as well continue to play a significant part, in roof sealing, for example.
A major disadvantage of aqueous emulsions is the physical drying of the materials, which becomes very slow particularly below a temperature of 15° C. Conversely, drying at the surface is comparatively rapid above 25° C., with the associated possibility of inclusions of water and, subsequently, formation of bubbles. In this way, weak points are formed in the coating, and can lead to leaks.
One-component, polyurethane-based sealing systems commonly comprise large amounts of solvent in order to lower the viscosity to an acceptable level for brush application or roll application in the roof region. Two-component polyurethane systems are very expensive by comparison and necessitate a complicated application technology. All polyurethane sealing systems include highly toxic isocyanate compounds, whose use is viewed critically in virtually all home applications, and also in many professional applications.
RTV-1 silicone coating formulations such as acetate systems or oxime systems give off elimination products in the course of curing that have a poor odor or even are harmful to health, such as acetic acid or oxime, for example. Other disadvantages of these materials are the poor adhesion to a large number of building materials, the poor recoatability, and the inadequate weathering stability.
One-component, moisture-curing coating materials based on MS Polymers (silane-terminated polyethers prepared by a particular process) are known in the form of sealing materials for application in the construction sector, from EP 1 695 989 A, WO 2007/093382, and WO 2008/077510.
Furthermore, EP 2135852 describes formulations based on silane-terminated polymers, prepared by reactions of polyols and isocyanate-functional polymers, that additionally comprise aminoalkylalkoxysilanes as well and also a relatively small amount, i.e., preferably 1% to 5% by weight, of alkylalkoxysilanes without an additional reactive organic function.
However, all of the known products have disadvantages, these disadvantages being massive in some cases. For instance, a feature common to all formulations based on conventional silane-crosslinking prepolymers is that they are relatively slow to react—in other words, for a reasonable skinning time and a passable volume curing, they usually require tin catalysts. MS Polymer-based formulations have the disadvantage, moreover, of possessing a substantial residual tack. This leads to rapid soiling and is unwanted as a consequence, particularly in applications in the roof region. In addition, in order to attain acceptable mechanical properties, MS Polymer-based formulations need to contain more than 25% by weight of MS Polymers, as a comparatively expensive formulation ingredient, as known from WO 2007/093382.
The major disadvantage of all the known systems, however, lies in the high viscosities of the silane-crosslinking prepolymers used. In order to obtain sprayable, rollable or spreadable formulations, therefore, it is generally necessary to add organic solvents and/or large amounts of plasticizers with a diluent effect. Solvents, as volatile organic constituents, are unwanted for environmental reasons. Plasticizers, for their part, may “exude” from the product over the course of time, which may likewise be extremely problematic.